Book Image

Mastering Go – Third Edition - Third Edition

By : Mihalis Tsoukalos
5 (2)
Book Image

Mastering Go – Third Edition - Third Edition

5 (2)
By: Mihalis Tsoukalos

Overview of this book

Mastering Go is the essential guide to putting Go to work on real production systems. This freshly updated third edition includes topics like creating RESTful servers and clients, understanding Go generics, and developing gRPC servers and clients. Mastering Go was written for programmers who want to explore the capabilities of Go in practice. As you work your way through the chapters, you’ll gain confidence and a deep understanding of advanced Go concepts, including concurrency and the operation of the Go Garbage Collector, using Go with Docker, writing powerful command-line utilities, working with JavaScript Object Notation (JSON) data, and interacting with databases. You’ll also improve your understanding of Go internals to optimize Go code and use data types and data structures in new and unexpected ways. This essential Go programming book will also take you through the nuances and idioms of Go with exercises and resources to fully embed your newly acquired knowledge. With the help of Mastering Go, you’ll become an expert Go programmer by building Go systems and implementing advanced Go techniques in your projects.
Table of Contents (17 chapters)
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Numeric data types

Go supports integer, floating-point, and complex number values in various versions depending on the memory space they consume—this saves memory and computing time. Integer data types can be either signed or unsigned, which is not the case for floating point numbers.

The table that follows lists the numeric data types of Go.

Data Type



8-bit signed integer


16-bit signed integer


32-bit signed integer


64-bit signed integer


32- or 64-bit signed integer


8-bit unsigned integer


16-bit unsigned integer


32-bit unsigned integer


64-bit unsigned integer


32- or 64-bit unsigned integer


32-bit floating-point number


64-bit floating-point number


Complex number with float32 parts


Complex number with float64 parts

The int and uint data types are special as they are the most efficient sizes for signed and unsigned integers on a given platform and can be either 32 or 64 bits each—their size is defined by Go itself. The int data type is the most widely used data type in Go due to its versatility.

The code that follows illustrates the use of numeric data types—you can find the entire program as numbers.go inside the ch02 directory of the book GitHub repository.

func main() {
    c1 := 12 + 1i
    c2 := complex(5, 7)
    fmt.Printf("Type of c1: %T\n", c1)
    fmt.Printf("Type of c2: %T\n", c2)

The previous code creates two complex variables in two different ways—both ways are perfectly valid and equivalent. Unless you are into mathematics, you will most likely not use complex numbers in your programs. However, the existence of complex numbers shows how modern Go is.

    var c3 complex64 = complex64(c1 + c2)
    fmt.Println("c3:", c3)
    fmt.Printf("Type of c3: %T\n", c3)
    cZero := c3 - c3
    fmt.Println("cZero:", cZero)

The previous code continues to work with complex numbers by adding and subtracting two pairs of them. Although cZero is equal to zero, it is still a complex number and a complex64 variable.

    x := 12
    k := 5
    fmt.Printf("Type of x: %T\n", x)
    div := x / k
    fmt.Println("div", div)

In this part, we define two integer variables named x and k—their data type is identified by Go based on their initial values. Both are of type int, which is what Go prefers to use for storing integer values. Additionally, when you divide two integer values, you get an integer result even when the division is not perfect. This means that if this is not what you want, you should take extra care—this is shown in the next code excerpt:

    var m, n float64
    m = 1.223
    fmt.Println("m, n:", m, n)
    y := 4 / 2.3
    fmt.Println("y:", y)
    divFloat := float64(x) / float64(k)
    fmt.Println("divFloat", divFloat)
    fmt.Printf("Type of divFloat: %T\n", divFloat)

The previous code works with float64 values and variables. As n does not have an initial value, it is automatically assigned with the zero value of its data type, which is 0 for the float64 data type.

Additionally, the code presents a technique for dividing integer values and getting a floating-point result, which is the use of float64(): divFloat := float64(x) / float64(k). This is a type conversion where two integers (x and k) are converted to float64 values. As the division between two float64 values is a float64 value, we get the result in the desired data type.

Running numbers.go creates the following output:

$ go run numbers.go
Type of c1: complex128
Type of c2: complex128
c3: (17+8i)
Type of c3: complex64
cZero: (0+0i)
Type of x: int
div 2
m, n: 1.223 0
y: 1.7391304347826086
divFloat 2.4
Type of divFloat: float64

The output shows that both c1 and c2 are complex128 values, which is the preferred complex data type for the machine on which the code was executed. However, c3 is a complex64 value because it was created using complex64(). The value of n is 0 because the n variable was not initialized, which means that Go automatically assigned the zero value of its data type to n.

After learning about numeric data types, it is time to learn about non-numeric data types, which is the subject of the next section.